Diversity and evolution of stem structure in Eleocharis (Cyperaceae)

Abstract

Eleocharis (Cyperaceae) includes more than 300 species of perennial or annual herbs, frequently found on poorly drained soils. The species are morphologicaly similar, and the taxonomy is difficult because their vegetative and reproductive structures are very reduced. Previous study on the stem architecture in the subgenus Limnochloa showed that anatomical features help in the interpretation of the evolution, taxonomy and ecological aspects of the group. Our objectives were to add new characters from the stem (= culm) structure, to explore the characters in a greater number of Eleocharis species, representatives of the other subgenera, and add these data in a new phylogenetic analysis with molecular data. The study covered 68 species obtained from herbaria and fixed material. In addition to the stem architecture, the internal organization of the tissues, the cross-section format, the presence or absence of stretched cells in aerenchyma air gaps and the plant size were included in the morphological analysis. Our data confirm that spongy aerenchyma pattern is the ancestral condition while the mixed and septate patterns occurred independent and punctually. Only the cross-section format was variable among specimens while the other characters were uniform and relevant for taxonomic use.

Characterization and evolution of the aerenchyma diaphragm of the stem in Eleocharis (Cyperaceae)

“…Most species only have one type of morphology in their diaphragm cells, but some have different morphological types in the same individual or among specimens. This is the case for E. montana and E. elegans, which present stems with septated architectures, and the morphology of the lateral diaphragm cells (present in the peripheral gaps) differs from that of the central gap diaphragm (Marcondes et al 2021).…”

“…The reconstruction of the ancestral states by parsimony was analyzed to evaluate the evolution of the characteristics resulting from the anatomical diagnosis. We employed the strict consensus tree used by Marcondes et al (2021) in the analysis of Eleocharis stem aerenchyma patterns; this tree was generated in the TNT (Tree analysis using New Technology) with ITS1, 5.8S, and ITS2 nuclear DNA sequences and trnC-ycf6 and ycf6-psbM from the chloroplast DNA. The reconstruction was done by parsimony in the program Mesquite v. 3.03 (Maddison & Maddison 2015).…”

“…It is known that most species of Eleocharis preferentially grow in environments with wet or flooded soils and can be found either totally or partially submerged (Trevisan & Boldrini 2008). Due to this plasticity in the environmental conditions needed for survival and reproduction, many emerging or submerged species present with highly developed aerenchyma tissue, both in the root and in the stem (Marcondes et al 2021).…”

“…The stem aerenchyma in Eleocharis is composed of air cavities, which are often septated by diaphragms (Metcalfe 1971;Marcondes et al 2021). According to the distribution of the cavities, two types of stem architecture are found in the subgenus Limnochloa species: spongy and septated (Hinchliff & Roalson 2009).…”

“…According to the distribution of the cavities, two types of stem architecture are found in the subgenus Limnochloa species: spongy and septated (Hinchliff & Roalson 2009). The spongy stem presents with several air columns in the central region of the organ, intersected transversally by diaphragms, while the septated stem has a central air column, which occupies most of the organ and is interrupted by large, transverse diaphragms (Marcondes et al 2021). These two patterns were recorded in 68 Eleocharis species, wherein spongy was the more frequent and was subdivided into two types by Marcondes et al (2021).…”